The present invention is directed to a method and apparatus for forming a continuous sheet of a molten material with particularly viscous, sticky properties. This molten material may be moldable, plasticized or a food product such as cheese. More specifically, the invention includes a manifold that discharges the molten material in a continuous layer upon the surface of a casting belt. This manifold comprises a roller, a hollow chamber with at least one open side and at least one inlet into the chamber.
Material such as processed cheese products present some difficulties in cutting or slicing because such material tends to cling to the cutting surfaces. For this reason, a process was developed in which such a material is melted and extruded into a thin sheet upon a surface such as a moving belt. In such a process, molten cheese is fed into a manifold, which distributes the molten cheese in a layer onto a continuously moving endless belt, which is commonly called a casting belt. Such a process, and the apparatus used in such a process, is described, for example, in U.S. Pat. Nos. 5,527,551 and 5,573,805, the entire content of which are incorporated herein by reference.
A standard manifold that may be used in such a process is also described, for example, in U.S. Pat. No. 4,790,242. In prior art manifolds, cheese is distributed from the manifold onto the casting belt. A fixed bar known as a xe2x80x9cnose barxe2x80x9d forms part of the manifold. The manifold distributes the cheese onto the casting belt between the nose bar and the surface of the casting belt (i.e., the space between the nose bar and the surface of the casting belt defines the thickness of the layer or film of cheese). Pressure is provided, through suitable pumps, to force the cheese to extrude between the surface of the belt and the nose bar. Since the casting belt is moving, the cheese is carried downstream of the nose bar on the surface of the casting belt thereby forming a continuously moving sheet of cheese. The sheet of cheese is further processed downstream in a manner known in the art. A standard manifold is divided into an upper and lower compartment and may even be further divided into a number of compartments in order to distribute evenly the pressure building up from the material coursing through the manifold. The manifold of the present invention, however, requires only one interior space, although additional compartments are not precluded from the invention.
Materials such as processed cheese products are now being created with more xe2x80x9cextremexe2x80x9d textures. These xe2x80x9cextremexe2x80x9d textures tend to be stickier and more viscous than other types of cheese. Because of this stickiness, it becomes more difficult to form a continuous sheet of material using the process and apparatus described in the prior art since the stickier material clogs the chambers of prior art manifolds and tends to tear while extruding onto the casting belt from a xe2x80x9cnose barxe2x80x9d or other such standard manifold. The viscosity also affects the processing because more viscous materials tend to tear as they exit from the nose bar.
Viscosity is a measurement of the flow properties of a product. Viscosity can be defined as the ratio of the xe2x80x9cshear forcexe2x80x9d applied to a material and the amount that the material is xe2x80x9cdeformedxe2x80x9d by this force. The deformation of the material is expressed as the xe2x80x9crate of shearxe2x80x9d. Therefore, viscosity is the relationship between shearing stress and rate of shear. Viscosity is temperature dependent and typically decreases as the temperature rises.
TABLE 1 below lists some common fluids and their viscosities, in addition to the viscosities of some of the products that could be processed using the method and apparatus of the current invention.
Therefore, a number of characteristics are desirable for a manifold dispensing such sticky or viscous material. Such a manifold must have a capability for receiving the starting material under pressure and distributing it evenly along the full length of the manifold and upon the casting belt. This distribution must be accomplished continuously to accommodate the high rate at which the material flows through the manifold. The manifold must facilitate distribution of the material in such a way that the material forms continuous sheets and does not tear as it is being deposited on the belt. The manifold should be easily assembled and disassembled for cleaning purposes. Finally, it would be advantageous if the manifold were interchangeable with a standard/prior art manifold (or other suitable manifold) so that more than one variety of manifold could be used with the same casting line and more than one variety of starting material could be processed.
The process by which such sticky, viscous starting material flows through the manifold should also accommodate the stickiness of the material. The material should flow through the manifold in such a manner and at a rate that is suitable for commercial processing and such that the manifold is not clogged.
Therefore, in view of the above, it is an object of the present invention to provide an apparatus and method which efficiently forms a continuous sheet of material from such a sticky or viscous starting material.
Another object of the present invention is to provide a manifold that accommodates such viscous starting material with minimal clogging and tearing.
The present invention provides a method and apparatus for forming a continuous sheet from a molten, viscous starting material, such as cheese. The invention may also be used to form other such moldable materials such as plastic.
More specifically, the invention includes a manifold, which discharges the starting material upon a surface, such as a casting belt. The manifold comprises a chamber with a hollow interior which receives the material, at least one inlet for feeding the material into the manifold and a roller which discharges the starting material upon a surface, such as a casting belt. The roller cooperates with the surface on which the material is distributed on in order to extrude the material in a smooth manner.
The manifold of the present invention is preferably mounted above the casting belt. The manifold is situated in such a way that the belt freely revolves underneath the manifold and the roller of the manifold freely revolves above the belt. A layer of material is formed between the belt and the roller.
A viscous sticky product run through the manifold of the present invention does not react as violently to pressure as in a standard manifold and therefore pressure is more constant as the material flows through the manifold.
In a preferred embodiment, the manifold of the present invention has top and bottom face plates, two end plates and upstream and downstream face plates; these face plates together form a chamber with a hollow interior. The bottom face is open to the casting belt along at least a part of its length. The downstream face is open to the roller along at least a part of its length.
The present invention, as well as the preferred embodiment thereof, will best be understood in view of the appended drawings, a brief description of which follows.